Power semiconductor device including well extension region and field-limiting rings

ABSTRACT

A drift region has a first conductivity type. A well region is at least partially included in an interface area, has an end portion between the interface area and an edge termination area, and has a second conductivity type. An extension region extends outward from the well region, is shallower than the well region, and has the second conductivity type. A plurality of field-limiting rings are provided outside the extension region in the edge termination area. Each of the field-limiting rings together with the drift region located on the inner side forms a unit structure. The field-limiting ring located closer to the outside has a lower proportion of a width to a width of the unit structure. The unit structure located closer to the outside has a lower average dose.

TECHNICAL FIELD

The present invention relates to a power semiconductor device.

BACKGROUND ART

According to Japanese Patent Application Laid-Open No. 2012-231011(Patent Document 1), an extraction region is disposed between atransistor region and a termination region disposed around thetransistor region in an insulated gate bipolar transistor (IGBT). Ap-type layer is provided on an n⁻-type drift layer in the extractionregion. The p-type layer is connected to an emitter electrode. A dummygate electrode is provided on the p-type layer with an insulating filmtherebetween. The dummy gate electrode is connected to a gate electrode.A current density easily increases in a boundary between the extractionregion and the termination region, namely, at an outer end of the p-typelayer, during a turn-off operation of the IGBT. As a result, thermalbreakdown may occur. A current breaking capability during the turn-offoperation is limited by this phenomenon.

According to the description in the above-mentioned Patent Document 1, alattice defect is introduced in the termination region. Thus, carrierannihilation in the termination region is facilitated, which reduces thecarrier concentration in the extraction region during the turn-offoperation of the IGBT. Therefore, the depletion from the p-type layertoward the collector is accelerated, and electric field strengthdecreases. As a result, the current breaking capability during theturn-off operation of the IGBT improves. On the other hand, no latticedefect is introduced in the extraction region. This intends to avoid anincrease in ON-state voltage. As described above, the technology in theabove-mentioned Patent Document 1 intends to improve the breakingcapability during the turn-off operation without adversely affecting theON-state voltage of the IGBT.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2012-231011

SUMMARY OF INVENTION Problems to be Solved by the Invention

Both of a low ON-state voltage and a high breaking capability can beobtained to some extent by the above-mentioned technology. However, atrade-off relationship between both of them in an IGBT still needsimprovements and further needs technologies. Other power semiconductordevices have similar challenges, and diodes, for example, needimprovements in the trade-off relationship between the low ON-statevoltage and the high breaking capability during a recovery operation.Additionally, reducing the manufacturing cost of the semiconductordevice is strongly required while the above-mentioned basic performanceis guaranteed. If the chip size of the semiconductor device can bereduced without sacrificing the performance, the number of chipsmanufactured from one wafer increases, allowing the manufacturing costto be reduced.

The present invention has been made in view of the above mentionedproblems, and an object thereof is to provide a power semiconductordevice having both of a small size and a high breaking capability.

Means to Solve the Problems

A power semiconductor device of the present invention has an activearea, an interface area provided around a periphery of the active area,and an edge termination area provided around a periphery of theinterface area. The power semiconductor device includes a semiconductorsubstrate, a first electrode, and a second electrode. The semiconductorsubstrate has a first surface and a second surface opposite to the firstsurface, the first surface and the second surface each being locatedacross the active area, the interface area, and the edge terminationarea. The semiconductor substrate includes a drift region of a firstconductivity type, a well region of a second conductivity type differentfrom the first conductivity type, an extension region of the secondconductivity type, and a plurality of field-limiting rings of the secondconductivity type. The drift region is provided across the active area,the interface area, and the edge termination area. The well region isprovided on the first surface, is at least partially included in theinterface area, and has an end portion on the first surface between theinterface area and the edge termination area. The extension regionextends outward from the well region on the first surface and isshallower than the well region. The field-limiting rings are provided onthe first surface outside the extension region in the edge terminationarea. The drift region is located on the inner side of each of thefield-limiting rings on the first surface, and each of thefield-limiting rings together with the drift region located on the innerside forms a unit structure. The field-limiting ring located closer tothe outside has a lower proportion of a width to a width of the unitstructure on the first surface. The unit structure located closer to theoutside has a lower average dose. The first electrode is provided in theactive area and contacts the first surface of the semiconductorsubstrate. The second electrode contacts the second surface of thesemiconductor substrate.

Effects of the Invention

In the power semiconductor device according to one aspect of the presentinvention, the unit structure that is formed of the field-limiting ringprovided in the edge termination area and that is located closer to theoutside has a lower average dose. This configuration can sufficientlysuppress the electric field strength in a smaller edge termination area.Thus, the chip size of the power semiconductor device can be reducedwithout sacrificing the area of the active area. Furthermore, the localtemperature rise in the boundary between the interface area and the edgetermination area can be suppressed. In other words, both of the smallchip size and the high static and dynamic breaking capability can beobtained.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view schematically showing a structure B of an IGBT asa power semiconductor device in a first embodiment of the presentinvention.

FIG. 2 is a schematic partial cross-sectional view taken along a II-IIline in FIG. 1 (IGBT 900B, structure B).

FIG. 3 is a plan view schematically showing a configuration of a secondsurface of a semiconductor substrate in FIG. 2.

FIG. 4 is a partial cross-sectional view showing a structure A of anIGBT in a comparative example when seen similarly to FIG. 2 (IGBT 900A,structure A).

FIG. 5 is a partial cross-sectional view schematically showing astructure C of an IGBT as a power semiconductor device in the firstembodiment of the present invention when seen similarly to FIG. 2 (IGBT900C, structure C).

FIG. 6 is a partial cross-sectional view schematically showing astructure D of an IGBT as a power semiconductor device in the firstembodiment of the present invention when seen similarly to FIG. 2 (IGBT900D, structure D).

FIG. 7 is a diagram of a circuit used for a simulation of a turn-offoperation of an IGBT.

FIG. 8 is a graphical representation showing turn-off waveforms obtainedfrom the simulation using the circuit in FIG. 7.

FIG. 9 is a graphical representation showing a temperature distributionof an upper surface S1 of a device in a D-D′ line each in the structureA (broken line) of the comparative example and the structure C (solidline) of the embodiment.

FIG. 10 is a graphical representation showing a relationship between apeak temperature T_(max) in FIG. 9 and a ballast-resistance-region width(L_(EEBR)).

FIG. 11 is a graphical representation showing each turn-off waveform ofa collector-emitter voltage V_(CE) and a collector current I_(C) in thecomparative example (broken line) having the structure A and in theembodiment (solid line) having the structure D.

FIG. 12A is a distribution chart showing a current potential and a holeconcentration when t=t_(ON) (FIG. 11) in the structure A as thecomparative example.

FIG. 12B is a distribution chart showing the current potential and thehole concentration when t=t_(peak) (FIG. 11) in the structure A as thecomparative example.

FIG. 13A is a distribution chart showing the current potential and thehole concentration when t=t_(ON) (FIG. 11) in the structure D as theembodiment.

FIG. 13B is a distribution chart showing the current potential and thehole concentration when t=t_(peak) (FIG. 11) in the structure D as theembodiment.

FIG. 14A is a distribution chart showing a carrier concentration insidethe device when t=t_(ON) (FIG. 11) in the structure A as the comparativeexample.

FIG. 14B is a distribution chart showing the carrier concentrationinside the device when t=t_(ON) (FIG. 11) in the structure D as theembodiment.

FIG. 15A is a distribution chart showing the carrier concentrationinside the device when t=t_(peak) (FIG. 11) in the structure A as thecomparative example.

FIG. 15B is a distribution chart showing the carrier concentrationinside the device when t=t_(peak) (FIG. 11) in the structure D as theembodiment.

FIG. 16A is a distribution chart showing the carrier concentrationinside the device when t=t_(tail) (FIG. 11) in the structure A as thecomparative example.

FIG. 16B is a distribution chart showing the carrier concentrationinside the device when t=t_(tail) (FIG. 11) in the structure D as theembodiment.

FIG. 17A is a distribution chart showing electric field strength insidethe device when t=t_(ON) (FIG. 11) in the structure A as the comparativeexample.

FIG. 17B is a distribution chart showing the electric field strengthinside the device when t=t_(ON) (FIG. 11) in the structure D as theembodiment.

FIG. 18A is a distribution chart showing the electric field strengthinside the device when t=t_(peak) (FIG. 11) in the structure A as thecomparative example.

FIG. 18B is a distribution chart showing the electric field strengthinside the device when t=t_(peak) (FIG. 11) in the structure D as theembodiment.

FIG. 19A is a distribution chart showing the electric field strengthinside the device when t=t_(tail) (FIG. 11) in the structure A as thecomparative example.

FIG. 19B is a distribution chart showing the electric field strengthinside the device when t=t_(tail) (FIG. 11) in the structure D as theembodiment.

FIG. 20 is a graphical representation showing an example ofrelationships between a proportion λ of a p-collector layer in thestructure D and various electrical characteristics, which are asaturation current density J_(C) (sat), an ON-state voltage V_(CE)(sat), a turn-off maximum breaking current density J_(C) (break), and amaximum breaking energy E_(SC) when a short circuit occurs.

FIG. 21 is a graphical representation showing relationships between adose in collector and the turn-off maximum breaking current densityJ_(C) (break) in the structure A (broken line) as the comparativeexample and the structure D (solid line) as the embodiment.

FIG. 22 is a graphical representation showing reverse bias safeoperating areas (RBSOAs) in the structure A (broken line) as thecomparative example and the structure D (solid line) as the embodiment.

FIG. 23 is a partial cross-sectional view showing a section of aconfiguration of a planar IGBT as another comparative example takenalong the II-II line (FIG. 1) (IGBT 900Z).

FIG. 24 is a graphical representation showing trade-off characteristicsbetween the ON-state voltage V_(CE) (sat) and a turn-off loss E_(OFF) inthe structure D (solid line) as the embodiment, the structure A (brokenline) as the comparative example, and the planar IGBT (alternate longand short dashed line) as the other comparative example.

FIG. 25 is a partial cross-sectional view schematically showing astructure E in a modification when seen similarly to FIG. 2 (IGBT 900E,structure E).

FIG. 26 is a partial cross-sectional view schematically showing astructure F in a modification (IGBT 900F, structure F).

FIG. 27 is a partial cross-sectional view schematically showing astructure G of an IGBT as a power semiconductor device in a secondembodiment of the present invention (IGBT 900G, structure G).

FIG. 28 is a partial cross-sectional view showing a region XXVIII inFIG. 27 in more detail.

FIG. 29 is a partial cross-sectional view schematically showing aconfiguration of a pseudo-well of field-limiting rings in FIG. 28.

FIG. 30A is a graphical representation showing simulation results ofeach turn-off waveform of the collector-emitter voltage V_(CE) and acollector current density J_(C) in the comparative example (broken line)having the structure A and in the embodiment (solid line) having thestructure G.

FIG. 30B is a graphical representation showing simulation results ofpeak temperatures inside the devices in the comparative example (brokenline) having the structure A and in the embodiment (solid line) havingthe structure G.

FIG. 31A is a distribution chart showing simulation results oftemperatures inside the devices in the comparative example having thestructure A and in the embodiment having the structure G.

FIG. 31B is a distribution chart showing simulation results of impactionization rates inside the devices in the comparative example havingthe structure A and in the embodiment having the structure G.

FIG. 32A is a graphical representation showing relationships between aposition X and electric field strength E_(edge) on the upper surface ofthe substrate each in a dynamic state (solid line) and a static state(broken line) of the comparative example having the structure A.

FIG. 32B is a graphical representation showing relationships between theposition X and the electric field strength E_(edge) on the upper surfaceof the substrate each in the dynamic state (solid line) and the staticstate (broken line) of the embodiment having the structure G.

FIG. 33 is a graphical representation showing relationships between aposition X_(edge) along a F-F′ line and electric field strength E in thestatic state of the comparative example (broken line) having thestructure A (FIG. 4) and the embodiment (solid line) having thestructure G (FIG. 27).

FIG. 34 is a graphical representation showing relationships between abreakdown voltage class V_(class) and a necessary width W_(edge) of anedge termination area in the comparative example having the structure Aand in the embodiment having the structure G.

FIG. 35 is a partial cross-sectional view schematically showing astructure H of a modification of FIG. 28 (IGBT 900H, structure H).

FIG. 36A is a partial cross-sectional view schematically showing astructure I of a modification of FIG. 28 (IGBT 900I, structure I).

FIG. 36B is a partial cross-sectional view schematically showing astructure J of a modification of FIG. 28 (IGBT 900J, structure J).

FIG. 37 is a partial cross-sectional view schematically showing aconfiguration of a diode as a power semiconductor device in a thirdembodiment of the present invention (diode 800A).

FIG. 38 is a partial cross-sectional view showing a configuration of adiode in a comparative example (diode 800Z).

FIG. 39 is a graphical representation showing waveforms of a voltageV_(AK) and a current density J_(A) during a recovery operation and apeak temperature T inside the device in each of the embodiment (solidline) and the comparative example (broken line).

FIG. 40A is a graphical representation showing a relationship between aposition X along a G-G′ line (FIGS. 37 and 38) and the current densityJ_(A) at a time t_(d) (FIG. 39) in each of the embodiment (solid line)and the comparative example (broken line).

FIG. 40B is a graphical representation showing a relationship betweenthe position X along the G-G′ line (FIGS. 37 and 38) and a temperature Tof an upper surface S1 of the device in each of the embodiment (solidline) and the comparative example (broken line).

FIG. 41 is a distribution chart showing relationships between widthsL_(ABR), W_(p0) in FIG. 37 and a temperature inside the device at thetime t_(d) (FIG. 39).

FIG. 42A is a distribution chart showing relationships between thewidths L_(ABR), W_(p0) in FIG. 37 and a current density inside thedevice at the time t_(d) (FIG. 39).

FIG. 42B is an enlarged view of each of the broken line regions in FIG.42A.

FIG. 43 is a graphical representation showing relationships between aproportion γ of an area S_(abr) of a ballast resistance region to anarea S_(active cell) of an active area and a maximum breaking currentdensity J_(A) (break) or an inside-device maximum temperature T_(max)during a recovery operation.

FIG. 44 is a plan view for describing the area S_(active cell) of theactive area and the area S_(arb) of the ballast resistance region.

FIG. 45A is a partial cross-sectional view schematically showing aconfiguration of a diode as a power semiconductor device in a fourthembodiment of the present invention (diode 800B).

FIG. 45B is a partial cross-sectional view showing a configuration of amodification of FIG. 45A (diode 800C).

FIG. 45C is a partial cross-sectional view showing a configuration of amodification of FIG. 45A (diode 800D).

FIG. 45D is a partial cross-sectional view showing a configuration of amodification of FIG. 45A (diode 800E).

FIG. 46A is a graphical representation showing simulation results ofwaveforms of a voltage V_(AK) and a current density J_(A) during arecovery operation in each of the embodiment (solid line) and thecomparative example (broken line).

FIG. 46B is a graphical representation showing simulation results of apeak temperature T inside the device during the recovery operation ineach of the embodiment (solid line) and the comparative example (brokenline).

FIG. 47A is a graphical representation showing a relationship between aposition X in a H-H′ line (FIG. 38) of the comparative example andelectric field strength E_(surface) when t=t₁ (FIGS. 46A and 46B).

FIG. 47B is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe electric field strength E_(surface) when t=t₂ (FIGS. 46A and 46B).

FIG. 47C is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe electric field strength E_(surface) when t=t₃ (FIGS. 46A and 46B).

FIG. 47D is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe electric field strength E_(surface) when t=t₄ (FIGS. 46A and 46B).

FIG. 48A is a graphical representation showing a relationship between aposition X in a H-H′ line (FIG. 45A) of the embodiment and the electricfield strength E_(surface) when t=t₁ (FIGS. 46A and 46B).

FIG. 48B is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and theelectric field strength E_(surface) when t=t₂ (FIGS. 46A and 46B).

FIG. 48C is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and theelectric field strength E_(surface) when t=t₃ (FIGS. 46A and 46B).

FIG. 48D is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and theelectric field strength E_(surface) when t=t₄ (FIGS. 46A and 46B).

FIG. 48E is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and theelectric field strength E_(surface) when t=t₅ (FIGS. 46A and 46B).

FIG. 48F is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and theelectric field strength E_(surface) when t=t₆ (FIGS. 46A and 46B).

FIG. 49A is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example anda current density j_(surface) when t=t₁ (FIGS. 46A and 46B).

FIG. 49B is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe current density j_(surface) when t=t₂ (FIGS. 46A and 46B).

FIG. 49C is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe current density j_(surface) when t=t₃ (FIGS. 46A and 46B).

FIG. 49D is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe current density j_(surface) when t=t₄ (FIGS. 46A and 46B).

FIG. 50A is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thecurrent density j_(surface) when t=t₁ (FIGS. 46A and 46B).

FIG. 50B is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thecurrent density j_(surface) when t=t₂ (FIGS. 46A and 46B).

FIG. 50C is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thecurrent density j_(surface) when t=t₃ (FIGS. 46A and 46B).

FIG. 50D is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thecurrent density j_(surface) when t=t₄ (FIGS. 46A and 46B).

FIG. 50E is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thecurrent density j_(surface) when t=t₅ (FIGS. 46A and 46B).

FIG. 50F is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thecurrent density j_(surface) when t=t₆ (FIGS. 46A and 46B).

FIG. 51A is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example anda temperature T_(surface) of an upper surface S1 of the device when t=t₁(FIGS. 46A and 46B).

FIG. 51B is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe temperature T_(surface) of the upper surface S1 of the device whent=t₂ (FIGS. 46A and 46B).

FIG. 51C is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe temperature T_(surface) of the upper surface S1 of the device whent=t₃ (FIGS. 46A and 46B).

FIG. 51D is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 38) of the comparative example andthe temperature T_(surface) of the upper surface S1 of the device whent=t₄ (FIGS. 46A and 46B).

FIG. 52A is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thetemperature T_(surface) of an upper surface S1 of the device when t=t₁(FIGS. 46A and 46B).

FIG. 52B is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thetemperature T_(surface) of the upper surface S1 of the device when t=t₂(FIGS. 46A and 46B).

FIG. 52C is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thetemperature T_(surface) of the upper surface S1 of the device when t=t₃(FIGS. 46A and 46B).

FIG. 52D is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thetemperature T_(surface) of the upper surface S1 of the device when t=t₄(FIGS. 46A and 46B).

FIG. 52E is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thetemperature T_(surface) of the upper surface S1 of the device when t=t₅(FIGS. 46A and 46B).

FIG. 52F is a graphical representation showing a relationship betweenthe position X in the H-H′ line (FIG. 45A) of the embodiment and thetemperature T_(surface) of the upper surface S1 of the device when t=t₆(FIGS. 46A and 46B).

FIG. 53 is a graphical representation for describing recovery safeoperating areas in the comparative example (indicated by triangles) andthe embodiment (indicated by circles).

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The same or corresponding portions have thesame reference numerals in the drawings, and their description will notbe repeated.

<First Embodiment>

About IGBT 900B

With reference to FIG. 1, an IGBT 900B (power semiconductor device) hasan active area AR1, an interface area AR2 provided around a periphery ofthe active area AR1, and an edge termination area AR3 provided around aperiphery of the interface area AR2. The active area AR1 is a portionhaving basic functions of the power semiconductor device, and a portionhaving basic functions of the IGBT in this embodiment. The edgetermination area AR3 is a portion for increasing breakdown voltagecharacteristics, stability, and reliability in a static state of thepower semiconductor device and for keeping breakdown strength in adynamic state. The interface area AR2 is a portion connecting the activearea AR1 and the edge termination area AR3 to each other and aparticularly important portion for keeping the breakdown strength in adynamic state.

The active area AR1 of the IGBT 900B includes emitter electrodes 13 ahaving an emitter potential, a gate pad 29 having a gate potential, anda gate wiring portion 28 extending from the gate pad 29.

With reference to FIG. 2, a structure (referred to as a structure B) ofthe IGBT 900B is described. FIG. 2 shows a cross-sectional structuretaken along a II-II line in FIG. 1. The IGBT 900B includes a substrateSB (semiconductor substrate), an emitter electrode 13 a (firstelectrode), a gate connecting electrode 13 b, electrodes 13 c, 13 d, acollector electrode 4 (second electrode), a gate electrode 22, a gatewiring layer 22 w, capacitor electrodes 23, 32, a trench insulating film10, interlayer insulating films 12 a, 12 b, and passivation films 14,15. In this embodiment, the substrate SB is made of silicon (Si). Thesubstrate SB has an upper surface S1 (first surface) and a lower surfaceS2 (second surface opposite to the first surface). The upper surface S1and the lower surface S2 are each located across the active area AR1,the interface area AR2, and the edge termination area AR3. The substrateSB includes an n⁻-drift layer 1 (drift region), an n-buffer layer 2, ap-collector layer 3 (collector region), an n⁺-emitter layer 5, ap⁺-layer 6, a p-base layer 8, an n-layer 24, and a p-guard ring 9.

The n⁻-drift layer 1 is provided across the active area AR1, theinterface area AR2, and the edge termination area AR3. The n⁻-driftlayer 1 has an n-type (first conductivity type) and has an impurityconcentration of, for example, approximately 1×10¹² to 1×10¹⁵ cm⁻³. Afloating zone (FZ) wafer manufactured by a FZ method or an epitaxialwafer manufactured by an epitaxial method may be prepared for then⁻-drift layer 1. In this case, a portion of the substrate SB except forthe n⁻-drift layer 1 may be formed by ion implantation and an annealingtechnique.

The n-layer 24 is provided between the n⁻-drift layer 1 and the p-baselayer 8. The n-layer 24 has the n-type, has an impurity peakconcentration at a concentration higher than the impurity concentrationin the n⁻-drift layer 1 and at a concentration lower than the p-baselayer 8, and has the impurity peak concentration of, for example,approximately 1×10¹⁵ to 1×10¹⁷ cm⁻³. A depth position that the n-layer24 reaches from the upper surface S1 of the substrate SB is deeper thanthe p-base layer 8 and has a depth of, for example, approximately 0.5 to1.0 μm deeper than the p-base layer 8.

The n-buffer layer 2 has a portion located between the n⁻-drift layer 1and the p-collector layer 3 in the active area AR1, and has a portionlocated between the n⁻-drift layer 1 and the collector electrode 4 inthe interface area AR2 and the edge termination area AR3 in thisembodiment. The n-buffer layer 2 has the n-type, has an impurityconcentration higher than the impurity concentration in the n⁻-driftlayer 1, and has an impurity peak concentration of, for example,approximately 1×10¹⁵ to 1×10¹⁷ cm⁻³. A depth position that the n-bufferlayer 2 reaches from the lower surface S2 of the substrate SB is, forexample, approximately 1.5 to 50 μm.

The n⁻-drift layer 1, the n-layer 24, and the buffer layer 2, which havebeen described above, as a whole form a region having the n-type (firstregion). In addition, one or both of the n-layer 24 and the n-bufferlayer 2 may be omitted.

The p-base layer 8 (second region) is provided on the region (firstregion) including the n⁻-drift layer 1 and the n-layer 24, and provideddirectly above the n-layer 24 in this embodiment. A depth position thatthe p-base layer 8 reaches from the upper surface S1 of the substrate SBis deeper than the n⁺-emitter layer 5 and shallower than the n-layer 24.The p-base layer 8 has a p-type (second conductivity type different fromthe first conductivity type) and has an impurity peak concentration of,for example, approximately 1×10¹⁶ to 1×10¹⁸ cm⁻³.

The n⁺-emitter layer 5 (third region) is provided on the p-base layer 8and disposed on the upper surface S1. The n⁺-emitter layer 5 has a depthof approximately 0.2 to 1.0 μm, for example. The n⁺-emitter layer 5 hasthe n-type and has an impurity peak concentration of, for example,approximately 1×10¹⁸ to 1×10²¹ cm⁻³.

The p⁺-layer 6 is provided on the p-base layer 8 and disposed on theupper surface S1. The p⁺-layer 6 has a surface impurity concentration ofapproximately 1×10¹⁸ to 1×10²¹ cm⁻³, for example. A depth position thatthe p⁺-layer 6 reaches from the upper surface S1 of the substrate SB ispreferably the same as or deeper than the n⁺-emitter layer 5.

The p-collector layer 3 is provided only in the active area AR1 andforms part of the lower surface S2. The p-collector layer 3 has thep-type and has a surface impurity concentration of, for example,approximately 1×10¹⁶ to 1×10²⁰ cm⁻³. The p-collector layer 3 has a depthof, for example, approximately 0.3 to 1.0 μm from the lower surface S2of the substrate SB.

The p-guard ring 9 is provided on the upper surface S1 and has thep-type. The p-guard ring 9 has a p-well region 9 a and a p-edge region 9b. The p-well region 9 a is connected to the emitter electrode 13 athrough the p⁺-layer 6 provided on the upper surface S1 in the activearea AR1. The p-well region 9 a is at least partially included in theinterface area AR2 and has an end portion on the upper surface S1between the interface area AR2 and the edge termination area AR3. Thep-well region 9 a further increases the breaking capability of the IGBT900B.

The p-edge region 9 b is included in the edge termination area AR3 andis located far from the interface area AR2. In addition, FIG. 2schematically shows only one p-edge region 9 b, but a plurality ofp-edge regions 9 b are designed so as to be disposed at an interval fromeach other according to voltage being maintained.

A gate trench TG and a capacitor trench TC are provided on the uppersurface S1 of the substrate SB in the active area AR1. A side wall ofthe gate trench TG faces each of the n⁻-drift layer 1 and the n-layer 24(first region), the p-base layer 8, and the n⁺-emitter layer 5. A sidewall of the capacitor trench TC faces each of the n⁻-drift layer 1, then-layer 24, and the p-base layer 8 in this embodiment. The capacitortrench TC located on the outermost side of the active area AR1 reachesthe inside of the p-well region 9 a of the p-guard ring 9. The trenchinsulating film 10 covers the gate trench TG and the capacitor trench TCof the substrate SB.

The gate electrode 22 has a portion filling the gate trench TG with thetrench insulating film 10 therebetween and faces the p-base layer 8between the n⁺-emitter layer 5 and the n-layer 24 (first region) withthe trench insulating film 10 between the p-base layer 8 and the gateelectrode 22. The capacitor electrode 23 has a portion filling thecapacitor trench TC with the trench insulating film 10 therebetween.Providing the capacitor electrode 23 suppresses a density of saturationcurrent in the IGBT 900B and suppresses an oscillation phenomenon ofgate voltage when a load on the IGBT 900B is short-circuited. Inaddition, the capacitor trench TC and the capacitor electrode 23 may beomitted.

The interlayer insulating film 12 a is provided on the upper surface S1of the substrate SB. The emitter electrode 13 a, the gate connectingelectrode 13 b, and the electrodes 13 c, 13 d are provided on theinterlayer insulating film 12 a. The emitter electrode 13 a is providedin the active area AR1 and contacts the upper surface S1 of thesubstrate SB. Specifically, the emitter electrode 13 a contacts each ofthe n⁺-emitter layer 5 and the p⁺-layer 6 through a contact holeprovided in the interlayer insulating film 12 a. The gate connectingelectrode 13 b contacts the gate wiring layer 22 w through a contacthole. Thus, the gate connecting electrode 13 b is short-circuited to thegate electrode 22 and thus has a gate potential. The electrode 13 ccontacts the p-well region 9 a through a contact hole. The electrode 13c may be short-circuited to the emitter electrode 13 a. The electrode 13d is a floating electrode and contacts the p-edge region 9 b through acontact hole in the IGBT 900B.

The interlayer insulating film 12 b is provided on the upper surface S1of the substrate SB. The interlayer insulating film 12 b insulates thesubstrate SB and the gate wiring layer 22 w from each other. Theinterlayer insulating film 12 b may have a portion located between partof the interlayer insulating film 12 a and the substrate SB.

The collector electrode 4 is provided on the lower surface S2 of thesubstrate SB. The collector electrode 4 contacts the p-collector layer 3in the active area AR1. The collector electrode 4 may contact then-buffer layer 2 (more generally, the above-described first region) inthe interface area AR2 and the edge termination area AR3, as shown inFIG. 2.

A channel stop structure CS is preferably provided in the edgetermination area AR3. In this embodiment, an n-region 34, a p-region 38,and an n⁺-region 35 are formed on the upper surface S1 of the substrateSB in the stated order. Further, a channel stop trench TS thatpenetrates these regions and reaches the n⁻-drift layer 1 is provided onthe upper surface S1. A channel stop electrode 32 is provided in thechannel stop trench TS with the trench insulating film 10 therebetween.An electrode 13 having a floating potential may be provided on thechannel stop electrode 32. Another structure may be used instead of thechannel stop structure CS described above, and a structure formed of then⁺-region 35 may simply be used, for example.

With reference to FIG. 3, if a proportion of an area of the p-collectorlayer 3 to the lower surface S2 of the substrate SB is set to be λ, λ ispreferably greater than or equal to 55% and less than or equal to 70%.In other words, 55≤100×(X_(p)×Y_(p))/(X_(n)×Y_(n))≤70 is preferablysatisfied. Herein, X_(n) and Y_(n) represent the chip size of the IGBT900B. When λ<55%, a hole injection from the p-collector layer 3 in theactive area AR1 of the IGBT is insufficient, and thus an ON-statevoltage (V_(CE) (sat)) increases. When λ>70%, electric field strength ofa weak spot (arrow WS in FIG. 2) due to a local temperature rise duringa turn-off operation of the IGBT as described below is not reducedbecause a carrier injection from the p-collector layer 3 occurs in an ONstate of the IGBT and causes carriers in the portion of the arrow WS,thereby reducing the breaking capability. Consequently, a value of λ hasan appropriate range according to a balance of the performance of theIGBT. In addition, a proportion of a total of the active area AR1 andthe interface area AR2 to the lower surface S2 preferably exceeds 70%and is, for example, approximately 75%.

(About IGBT 900A)

With reference to FIG. 4, an IGBT 900A in an comparative example isdifferent from the IGBT 900B and has the p-collector layer 3 in anotherarea in addition to the active area AR1. Specifically, the p-collectorlayer 3 is provided on the entire lower surface S2 of the substrate SB.The configuration except for this is almost the same as that of the IGBT900B described above.

In the IGBT 900A, repetitive turn-off operations are likely toparticularly cause a local temperature rise in the boundary between theactive area AR1 and the interface area AR2 on the upper surface S1 ofthe substrate SB, namely, the arrow WS (FIG. 2). This phenomenon maylimit the breaking capability of the IGBT 900A.

(About Action Effects of IGBT 900B)

The p-collector layer 3 is not provided in the edge termination area AR3and the interface area AR2 in the IGBT 900B shown in FIG. 2 unlike theIGBT 900A. This suppresses a temperature rise in the arrow WS in thebreaking operation of the IGBT 900B. The active area AR1 has the sameconfiguration as that in the IGBT 900A and thus is not adverselyaffected in such a manner that ON-state voltage increases. Accordingly,the IGBT 900B has both of a low ON-state voltage and a high breakingcapability.

(About IGBT 900C)

With reference to FIG. 5, a contact (see FIG. 4) of the electrode 13 cto the p-well region 9 a is not provided in an IGBT 900C. The p-wellregion 9 a has an electrical path that connects the emitter electrode 13a to an end portion (arrow WS in the diagram) of the p-well region 9 awith the p-type region on the upper surface S1. This electrical pathcrosses the interface area AR2 between the active area AR1 and the edgetermination area AR3 and has a resistance region having a widthL_(EEBR). The entire resistance region is covered with the interlayerinsulating film 12 b. The width L_(EEBR), which will be described belowin detail, is set so as to suppress a local temperature rise in one ofends of the resistance region by sharing the temperature rise at boththe ends during the breaking operation of the IGBT. A local temperaturerise occurs in the portion of the arrow WS in the IGBT 900A (FIG. 4),whereas the resistance region is provided in the IGBT 900C to share atemperature rise at both the ends of the resistance region. Such effectis referred to as a ballast resistance, and the resistance region isalso referred to as a ballast resistance region.

The configuration except for the above-described configuration is almostthe same as that of the IGBT 900B described above.

Under the operation of the IGBT 900C, a local temperature rise occursnot only in a position of one end (right end of the width L_(EEBR) inthe diagram) of the ballast resistance region but also in a position ofanother end (left end of the width L_(EEBR) in the diagram), theposition of the one end corresponding to the position of the boundarybetween the interface area AR2 and the edge termination area AR3 (arrowWS in FIG. 5). This causes the temperature rise to be distributed, andthus the local temperature rise in the arrow WS can be reduced. Herein,the active area AR1 has the same configuration as that in the IGBT 900A,so that the ON-state voltage is not adversely affected. Accordingly, theIGBT 900C has both of a low ON-state voltage and a high breakingcapability.

(About IGBT 900D)

With reference to FIG. 6, an IGBT 900D has the characteristics of eachof the IGBTs 900B, 900C described above. Specifically, the p-collectorlayer 3 is provided only in the active area AR1 similarly to the IGBT900B. Moreover, the ballast resistance region having the width L_(EEBR)is provided similarly to the IGBT 900C. The configuration except forthis is almost the same as that of the IGBT 900B or the IGBT 900Cdescribed above. The IGBT 900D can have both of a low ON-state voltageand a high breaking capability by the action of each of the IGBTs 900Band 900C described above.

(Verification of Effects of IGBT 900C)

FIG. 7 is a diagram of a circuit used for a simulation of a turn-offoperation of an IGBT of 4500V class. FIG. 8 shows turn-off waveformsobtained from using the circuit in FIG. 7, namely, relationships betweena time t and a collector-emitter voltage V_(CE). FIG. 9 shows atemperature distribution in the X coordinate along a D-D′ line (FIGS. 4and 5) immediately before a collector current density J_(C) abruptlydecreases (at the point indicated by an arrow in FIG. 8) each in theIGBT 900A (broken line) as the comparative example and the IGBT 900C(solid line) as the embodiment in which L_(EEBR)=200 μm. FIG. 10 shows arelationship between a peak temperature T_(max) inside the device andL_(EEBR).

As seen from the simulation results, the peak temperature T_(max) insidethe device can be suppressed by sharing voltage in the ballastresistance region, and when L_(EEBR) is particularly set to be greaterthan or equal to 100 μm, T_(max) can be set to be less than or equal to800 K. As described above, it is clear that providing the ballastresistance region can prevent breakdown due to heat generation, that isto say, providing the ballast resistance region can increase thebreaking capability of the IGBT.

(Verification of Effects of IGBT 900B and IGBT 900D)

FIG. 11 shows an example of each turn-off waveform in the IGBT 900A(broken line) as the comparative example and in the IGBT 900D (solidline) as the embodiment. FIG. 12A shows a current potential and a holeconcentration in an ON state of the comparative example (t_(ON) in FIG.11) from the view of FIG. 4. FIG. 12B shows the current potential andthe hole concentration at a peak of a collector-emitter voltage V_(CE)during turn-off of the comparative example (t_(peak) of the broken linein FIG. 11) from the view of FIG. 6. FIG. 13A shows the currentpotential and the hole concentration in an ON state of the embodiment(t_(ON) in FIG. 11) from the view of FIG. 6. FIG. 13B shows the currentpotential and the hole concentration at a peak of the collector-emittervoltage V_(CE) during turn-off of the embodiment (t_(peak) of the solidline in FIG. 11) from the view of FIG. 4. FIGS. 14A and 14B respectivelyshow a carrier concentration inside the device when t=t_(ON) (FIG. 11)in the comparative example and the embodiment. FIGS. 15A and 15Brespectively show the carrier concentration inside the device whent=t_(peak) (FIG. 11) in the comparative example and the embodiment.FIGS. 16A and 16B respectively show the carrier concentration inside thedevice when t=t_(tail) (FIG. 11) in the comparative example and theembodiment. FIGS. 17A and 17B respectively show electric field strengthinside the device when t=t_(ON) (FIG. 11) in the comparative example andthe embodiment. FIGS. 18A and 18B respectively show the electric fieldstrength inside the device when t=t_(peak) (FIG. 11) in the comparativeexample and the embodiment. FIGS. 19A and 19B show the electric fieldstrength inside the device when t=t_(tail) (FIG. 11) in the comparativeexample and the embodiment.

As seen from FIGS. 12A, 12B, 13A, 13B, 14A, 14B, 15A, 15B, 16A, and 16B,the carrier concentration of the IGBT 900D (structure D) in theembodiment is almost the same as that in the active area AR1 of the IGBT900A in the comparative example, but the carrier concentration in theedge termination area AR3 of the IGBT 900D is lower than that of theIGBT 900A. The reason is conceivable that a hole injection from thep-collector layer 3 does not occur in the interface area AR2 and theedge termination area AR3. It is conceivable that this action is alsosimilar to that in the IGBT 900B (structure B) having the same collectorstructure as the IGBT 900D.

Moreover, as shown in FIGS. 17A, 17B, 18A, 18B, 19A, and 19B, theabove-mentioned action accelerates electric field relaxation anddepletion in the interface area AR2 and the edge termination area AR3during the turn-off operation. Particularly with reference to FIGS. 19Aand 19B, the electric field relaxation in the boundary between theinterface area AR2 and the edge termination area AR3 on the uppersurface S1 contributes to an improvement in the breaking capability.

With reference to FIG. 20, a proportion λ of an area of the p-collectorlayer 3 to the lower surface S2 of the substrate SB needs to beappropriate to keep a suitable balance between a high breakingcapability and a low ON-state voltage. In the diagram, λ=100%corresponds to the collector structure of the IGBT 900A in thecomparative example. As seen from the results shown, λ is preferablygreater than or equal to 55% and less than or equal to 70%. Setting avalue of λ from 55 to 70% can both achieve a high turn-off maximumbreaking current density J_(C) (break) and no adverse effect ofincreasing an ON-state voltage V_(CE) (sat).

The result that λ=75% in the graph corresponds to the structure in whichthe p-collector layer 3 is provided in the active area AR1 and theinterface area AR2 and not provided in the edge termination area AR3.When λ is increased to 75%, a noticeable decrease is seen in theturn-off maximum breaking current density J_(C) (break). This indicatesthat providing no p-collector layer 3 in the interface area AR2 isimportant in order to increase J_(C) (break).

FIG. 21 shows an example of relationships between a dose of ionimplantation for forming the p-collector layer 3 and the turn-offmaximum breaking current density J_(C) (break) in the IGBT 900A (brokenline) as the comparative example and the IGBT 900D (solid line) as theembodiment. FIG. 22 shows relationships between a power supply voltageV_(CC) and a saturation current density J_(C) (sat) or a maximum powerdensity P_(max), as RBSOAs in the comparative example (broken line) andthe embodiment (solid line). A region surrounded by each line in FIG. 22is a region called a recovery safe operating area (SOA). The breakingcapability during the turn-off of the IGBT is affected by efficiency ofthe hole injection from the p-collector layer 3. A dose in thep-collector layer 3 is a parameter for controlling trade-offcharacteristics between the ON-state voltage V_(CE) (sat) and a turn-offloss E_(OFF) in the IGBT. Even if the dose in the p-collector layer 3 isadjusted to control the trade-off characteristics between V_(CE) (sat)and E_(OFF), the embodiment (solid line) can obtain J_(C) (break) higherthan that in the comparative example (broken line) as seen from FIG. 21and is the excellent IGBT having a low dependence of the dose in thep-collector layer 3 on J_(C) (break). Moreover, FIG. 22 indicates theexcellent effects of the embodiment that expands the RBSOA and increasesthe power density for breaking during the turn-off.

Table 1 below provides a summary of relationships between structuralcharacteristics of the IGBTs 900A to 900D (structures A to D) and theturn-off maximum breaking current density J_(C) (break) with referenceto a rated current density J_(C) (rated).

TABLE 1 Back Surface Ballast Structure of Resis- J_(C) (break) @Structure Interface Area tance V_(CC) = 3600 V A (Comparative Ex-p-collector No 1.0 J_(C) (rated) ample) (IGBT 900A) B (IGBT 900B)n-buffer No 4.0 J_(C) (rated) C (IGBT 900C) p-collector Yes 3.0 J_(C)(rated) D (IGBT 900D) n-buffer Yes ≥7.0 J_(C) (rated)   

As shown above, the structures B to D (IGBTs 900B to 900D) have J_(C)(break), namely, the turn-off breaking capability, higher than that inthe structure A (IGBT 900A). The structure D (IGBT 900D) particularlyhas the remarkably high capability.

FIG. 23 shows a configuration of an IGBT 900Z as another comparativeexample. The IGBT 900Z is different from the IGBTs 900A to 900Ddescribed above and includes a planar gate electrode 11. FIG. 24 showsthe trade-off characteristics between the ON-state voltage V_(CE) (sat)and the turn-off loss E_(OFF) in the IGBT 900D (solid line) as theembodiment and the IGBT 900A (broken line) and the IGBT 900Z (alternatelong and short dashed line) as the comparative examples. It is clearfrom the results that the IGBT 900D has the high turn-off breakingcapability as described with reference to FIG. 21 and Table 1 and alsohas the excellent trade-off characteristics between the ON-state voltageV_(CE) (sat) and the turn-off loss E_(OFF).

(About IGBT 900E and IGBT 900F)

With reference to FIG. 25, in an IGBT 900E as a modification of the IGBT900D (FIG. 6), the n-buffer layer 2 is provided only in the active areaAR1 and not provided in the interface area AR2 and the edge terminationarea AR3. The pattern of the n-buffer layer 2 may be the same as thepattern of the p-collector layer 3. In addition, such structure may becombined with the IGBT 900B instead of the IGBT 900D.

With reference to FIG. 26, in an IGBT 900F as a modification of the IGBT900B (FIG. 2), the active area AR1 has a Metal Insulator Semiconductor(MIS) structural portions (left portion and right portion in thediagram) in which a MIS structural cell is disposed and a non-MISstructural portion (central portion in the diagram) in which no MISstructural cell is disposed. In the diagram, the central portion is aportion AR1 g in which the gate wiring portion 28 and the gate pad 29(FIG. 1) are provided in the active area AR1. The p-collector layer 3 isnot provided in the portion AR1 g, and, as a result, the buffer layer 2contacts the collector electrode 4 on the lower surface S2. The MISstructure is typically a metal oxide semiconductor (MOS) structure. Suchstructure also has the same effects as those of the IGBT 900D.

<Second Embodiment>

With reference to FIG. 27, a structure (referred to as a structure G) ofan IGBT 900G in this embodiment is described.

A substrate SB in the structure G includes an n⁻-drift layer 1, ann-buffer layer 2, a p-collector layer 3, an n⁺-emitter layer 5, ap⁺-layer 6, a p-base layer 8, an n-layer 24, a p-well region 9 a, ap⁻-extension region 9 j, and a plurality of p⁻-field-limiting rings 9 g.The p-well region 9 a is covered with an interlayer insulating film 12 bin an interface area AR2.

The p⁻-extension region 9 j extends outward (to the right side in thediagram) from the p-well region 9 a on an upper surface S1 and isshallower than the p-well region 9 a. The p⁻-extension region 9 j has ap-type and has a peak impurity concentration and a surface impurityconcentration lower than those of the p-well.

Further, with reference to FIG. 28, the p⁻-field-limiting rings 9 g havethe p-type. The p⁻-field-limiting rings 9 g are provided on the uppersurface S1 outside the p⁻-extension region 9 j in an edge terminationarea AR3. The n⁻-drift layer 1 is located on the inner side of each ofthe p⁻-field-limiting rings 9 g on the upper surface S1, and each of thep⁻-field-limiting rings 9 g together with the n⁻-drift layer 1 locatedon the inner side forms corresponding unit structures US1 to US6(collectively referred to as USs). A width W_(cellpitch) of the unitstructure US is a fixed value. The p⁻-field-limiting ring 9 g locatedcloser to the outside (right side in the diagram) has a lower proportionof a width W_(p−) to the width W_(cellpitch) of the unit structure US onthe upper surface S1. The unit structure US located closer to theoutside has a lower average dose. Herein, the average dose in the unitstructure US is a numeric value that the number of ions implanted forforming the p⁻-field-limiting ring 9 g of the specific unit structure USis divided by an area of the unit structure US on the upper surface S1.In other words, the average dose in the unit structure US is a dose froma macroscopic perspective that ignores the internal structure of theunit structure US.

In the structure illustrated in FIG. 28, each of the unit structures USson the upper surface S1 of the substrate SB has the fixed widthW_(cellpitch). The p⁻-field-limiting ring 9 g located closer to theoutside (right side in the diagram) has the smaller W_(p−) on the uppersurface S1. To obtain the unit structures USs, an ion implantation maskhaving a plurality of openings at a fixed pitch may be used in an ionimplantation step of forming the field-limiting rings 9 g, for example,the opening located closer to the outside having a smaller width. Thefield-limiting ring 9 g having the smaller width when subjected to theion implantation eventually has a smaller depth after activationannealing, namely, after diffusion. FIG. 28 shows as if thep⁻-field-limiting rings 9 g are individual, but approximately ⅓ to ½ ofthe plurality of p⁻-field-limiting rings 9 g that have been originallyformed as impurity regions are connected to the p⁻-extension region 9 jdue to the activation annealing.

The width W_(p−) is preferably decreased by a fixed dimension for eachunit structure US toward the outside. In this case, an average dose inthe unit structure US linearly changes for each unit structure US towardthe outside under the condition that the width W_(cellpitch) is fixed.From a macroscopic perspective that ignores the internal structure ofthe unit structure US, a pseudo-p⁻ well 9 p is supposed to be providedsuch that an impurity concentration thereof is decreased with a fixedconcentration gradient in a direction of the arrow in the diagram, asshown in FIG. 29. In this configuration, on the upper surface S1, thep⁻-extension region 9 j (FIG. 27) has the almost fixed impurityconcentration while the pseudo-p⁻ well 9 p located outside thep⁻-extension region 9 j has the impurity concentration linearlydecreased toward the outside.

The configuration except for the above-described configuration is almostthe same as the configuration of the IGBT 900D in the first embodimentdescribed above, so that the same or corresponding components have thesame references, and their description will not be repeated.

In this embodiment, the unit structures USs are formed of thep⁻-field-limiting rings 9 g provided in the edge termination area AR3,and the unit structure US located closer to the outside has the loweraverage dose. This configuration can sufficiently suppress the electricfield strength in the interface area AR2 even if the edge terminationarea AR3 is smaller than the edge termination area AR3 in which theaverage dose is not controlled as described above. Thus, a temperaturerise can be suppressed in the boundary between the active area AR1 andthe interface area AR2 without greatly sacrificing the area of theactive area AR1. In other words, both of a low ON-state voltage and ahigh breaking capability can be obtained. Particularly in a case whereeach of the unit structures USs have the fixed width W_(cellpitch), bothof the low ON-state voltage and the high breaking capability can beobtained with more reliability.

Next, the verification results of the action effects described above aredescribed below.

FIG. 30A shows the simulation results of each turn-off waveform of thecollector-emitter voltage V_(CE) and the collector current density J_(C)in the IGBT 900A (FIG. 4) as the comparative example (broken line) andin the IGBT 900G (FIG. 27) as the embodiment (solid line). FIG. 30B is agraphical representation showing simulation results of peak temperaturesinside the devices in the comparative example (broken line) and theembodiment (solid line). “x” in FIGS. 30A and 30B represents breakage ofthe device. The simulation results of the internal state of the deviceat the point indicated by an arrow in FIG. 30A are shown in more detailin FIGS. 31A and 31B. FIG. 31A shows temperatures inside the devices inthe comparative example and the embodiment. FIG. 31B shows impactionization rates inside the devices in the comparative example and theembodiment. In FIGS. 31A and 31B, the broken line portion indicated byan arrow corresponds to the interface area AR2. As seen from thesimulation results, a local temperature rise in the interface area AR2is lower in the embodiment than that in the comparative example. Thus,the embodiment conceivably has the smaller temperature rise inside thedevice during the turn-off operation of the IGBT and the higher breakingcapability.

FIG. 32A shows relationships between a position X and electric fieldstrength E_(edge) on the upper surface of the substrate each in adynamic state (solid line) and a static state (broken line) of the IGBT900A (FIG. 4) as the comparative example. FIG. 32B shows relationshipsbetween the position X and the electric field strength E_(edge) on theupper surface of the substrate each in the dynamic state (solid line)and the static state (broken line) of the IGBT 900G (FIG. 27) as theembodiment. Herein, the condition for the static state is that acollector-emitter voltage V_(CES)=3600 V, a gate voltage V_(G)=0 V, anda temperature T=423 K. For the dynamic state, the state indicated by thearrow in FIG. 30A is used. As seen from the results, the electric fieldstrength E_(edge) around the boundary between the interface area AR2 andthe edge termination area AR3 is lower in not only the static state butalso the dynamic state of the IGBT 900G than that in the IGBT 900A. Inthis manner, the electric field strength is more suppressed in the IGBT900G than that in the IGBT 900A, and thus the impact ionization issuppressed (FIG. 31B), which conceivably suppresses the localtemperature rise (FIG. 31A).

As described above, this embodiment can increase the turn-off breakingcapability. Moreover, the active area AR1 can have the sameconfiguration as that in the IGBT 900A (FIG. 4) in the comparativeexample, so that the other characteristics are not particularlyadversely affected. Thus, this embodiment can also obtain the similarcharacteristics to those of the IGBT 900D (FIG. 6) described above.

Further, this embodiment can reduce the width of the edge terminationarea AR3. According to estimates by the simulation, the widthmeasurement can be reduced by approximately 40 to 50%. This will bedescribed below.

FIG. 33 shows relationships between a position X_(edge) along a F-F′line and electric field strength E in the IGBT 900A (FIG. 4) as thecomparative example (broken line) and in the IGBT 900G (FIG. 27) as theembodiment (solid line) under the conditions that a collector-emittervoltage V_(CES)=4500 V and a temperature T=298 K. As seen from theresults, when the comparative example and the embodiment keep the samecollector-emitter voltage V_(CES), the embodiment suppresses theelectric field strength E more (see the down arrow in the diagram) thanthe comparative example while suppressing the measurement necessary forthe position X_(edge) (see the left arrow in the diagram).

FIG. 34 is a graphical representation showing relationships between abreakdown voltage class V_(class) and a necessary width W_(edge) of theedge termination area AR3 in the comparative example (broken line) andthe embodiment (solid line). The necessary width W_(edge) of the edgetermination area AR3 can be more reduced by 40 to 50% in the embodimentthan that in the comparative example regardless of the breakdown voltageclass V_(class). In other words, the device structure of FIG. 27 in thisembodiment allows for chip-size shrinking effects of reducing X_(n) andY_(n) being the chip size of the semiconductor device shown in FIG. 3without changing the size of the active area AR1 occupied in thesemiconductor device. Specifically, this embodiment can increase thenumber of semiconductor devices (the number of theoretical chips) perwafer in which the semiconductor devices are formed and can reduce thecost of the chip.

Next, a modification is described below. With reference to FIG. 35, anIGBT 900H includes a floating electrode 13 e on each of thep⁻-field-limiting rings 9 g with the interlayer insulating films 12 a,12 b therebetween. Each of the floating electrodes 13 e is disposedwithin the p⁻-field-limiting ring 9 g located directly below thefloating electrode 13 e in a width direction (lateral direction in FIG.35) with the interlayer insulating films 12 a, 12 b therebetween. Withreference to FIG. 36A, in an IGBT 900I, a gate connecting electrode 13 b(see FIG. 27) extends to the p⁻-extension region 9 j with the interlayerinsulating films 12 a, 12 b, which cover the p⁻-extension region 9 j,between the gate connecting electrode 13 b and the p⁻-extension region 9j. It should be noted that the gate connecting electrode 13 b is formedso as to be located on the inner side of the p⁻-extension region 9 j andthe floating electrodes 13 e are formed so as to be located within thep⁻-field-limiting rings 9 g as described above in the width direction(lateral direction in the diagram). With reference to FIG. 36B, an IGBT900J has the structure of the IGBT 900I (FIG. 36A) from which thefloating electrodes 13 e are omitted. These structures can obtain thehigher breakdown voltage and the higher breaking capability while adistribution of the electric field strength in the edge termination areaAR3 characterized by the IGBT 900G in FIGS. 32B, 33 does not vary withtime and is stabilized in a range of operation temperatures thatguarantee the performance of the IGBT even if electrical stress isapplied.

<Third Embodiment>

This embodiment gives descriptions of a diode having the sameconfiguration as the ballast resistance region (FIG. 5: the portionhaving the width L_(EEBR) in the p-well region 9 a in the IGBT 900C)described in the first embodiment. In addition, part of the descriptionsof the same configuration as the IGBT 900C will not be repeated.

With reference to FIG. 37, a diode 800A (power semiconductor device) inthis embodiment has an active area AR1, an interface area AR2 providedaround a periphery of the active area AR1, and an edge termination areaAR3 provided around a periphery of the interface area AR2 similarly tothe IGBT shown in FIG. 5. The active area AR1 is a portion having thebasic functions of the diode in this embodiment.

The diode 800A includes a substrate SB (semiconductor substrate), ananode electrode 13 (first electrode), a cathode electrode 4D (secondelectrode), and an interlayer insulating film 12. The substrate SBincludes an n⁻-drift layer 1 (drift region), an n-buffer layer 2, ananode layer 8D, a p-guard ring 9, a p-layer 26, an n⁺-layer 27, and ann⁺-region 35. The anode electrode 13 is provided in the active area AR1and contacts the anode layer 8D on an upper surface S1 of the substrateSB. The anode layer 8D is provided on the n⁻-drift layer 1. The cathodeelectrode 4D contacts a semiconductor layer formed of the p-layer 26 andthe n⁺-layer 27 on a lower surface S2 of the substrate SB. The n⁺-layer27 is provided only in the active area AR1. The n-buffer layer 2 isprovided between the semiconductor layer and the n⁻-drift layer 1. Theinterlayer insulating film 12 has openings in the active area AR1.

The anode layer 8D has a depth of approximately 0.5 to 10 μm, forexample. The anode layer 8D has a p-type and has a peak impurityconcentration of, for example, approximately 1×10¹⁶ to 1×10²⁰ cm⁻³. Thep-guard ring 9 has a depth of approximately 5 to 10 μm, for example. Thep-guard ring 9 has a peak impurity concentration of approximately 1×10¹⁶to 1×10²⁰ cm³, for example. The n⁺-region 35 has a depth ofapproximately 0.2 to 1 μm, for example. The n⁺-region 35 has an n-typeand has a peak impurity concentration of, for example, approximately1×10¹⁸ to 1×10²¹ cm⁻³. The p-layer 26 has a depth of approximately 0.3to 5 μm, for example. The p-layer 26 has a surface impurityconcentration of approximately 1×10¹⁶ to 1×10²⁰ cm⁻³, for example. Then⁺-layer 27 has a depth of approximately 0.3 to 5 μm, for example. Then⁺-layer 27 has a surface impurity concentration of approximately 1×10¹⁸to 1×10²⁰ cm⁻³, for example.

A p-well region 9 a in the diode 800A forms an electrical path thatconnects the anode electrode 13 to an end portion (right end in thediagram) of the p-well region 9 a with the p-type region on the uppersurface S1. This electrical path crosses the interface area AR2 betweenthe active area AR1 and the edge termination area AR3 and has aresistance region having a width L_(ABR). The entire resistance regionis covered with the interlayer insulating film 12. The p-well region 9 ahas a width W_(p0). The outer peripheral end of the n⁺-layer 27 and theboundary between the interface area AR2 and the edge termination areaAR3 are spaced by a distance having a width W_(GR) therebetween.

The widths L_(ABR), W_(p0), and W_(GR) are important parameters in thedesign of the diode 800A. The width L_(ABR) is set so as to obtain aballast resistance effect of sharing a temperature rise at both ends ofa resistance region during a recovery operation of the diode to suppressa local temperature rise in one of the ends. Specifically, a temperaturerise due to a local current concentration at an arrow WS shown in FIG.37 is shared, to thereby suppress a local temperature rise. In thisrespect, the width L_(ABR) is specifically greater than or equal to 100μm.

The ballast resistance region described above is not provided in a diode800Z (FIG. 38) in a comparative example. FIG. 38 schematically shows onep-edge region 9 b, but there are a plurality of p-edge regions 9 bsimilarly to FIG. 37. In the diode 800Z, a local temperature rise islikely to occur in the boundary between the interface area AR2 and theedge termination area AR3, namely, an arrow WS, on the upper surface S1of the substrate SB during a recovery operation. This phenomenon limitsthe breaking capability of the diode 800Z.

In contrast, this embodiment suppresses a local temperature rise due toa concentration of current in the boundary between the interface areaAR2 and the edge termination area AR3 by distributing the current in theballast resistance region corresponding to the position of the boundarybetween the interface area AR2 and the edge termination area AR3, asdescribed below with reference to FIG. 40A, during the recoveryoperation of the diode. Herein, the active area AR1 can have the sameconfiguration as that in the conventional diode, so that an adverseeffect such as an increase in ON-state voltage is not seen. As describedabove, similarly to the IGBT 900C, the diode 800A also has both of thelow ON-state voltage and the high breaking capability.

Next, the verification results of the action effects described above aredescribed below.

FIG. 39 shows waveforms of a voltage V_(AK) and a current density J_(A)during a recovery operation and a peak temperature T inside the devicein each of the diode 800A as the embodiment (solid line) and the diode800Z as the comparative example (broken line). FIG. 40A shows arelationship between a position X along a G-G′ line (FIGS. 37 and 38)and the current density J_(A) at a time t_(d) (FIG. 39) in each of theembodiment (solid line) and the comparative example (broken line), andFIG. 40B shows a relationship between the position X and a temperatureT. In the comparative example (broken line) in which the ballastresistance region is not provided, a concentration of the currentdensity J_(A) occurs at the end portion of the interface area AR2located around the boundary between the interface area AR2 and the edgetermination area AR3, and a local rise in the temperature T occurs. As aresult, as shown in FIG. 39, the diode 800Z fails to complete thebreaking operation, leading to breakage. In contrast, in the diode 800A,the current density J_(A) is distributed in the interface area AR2without being extremely concentrated, and there exists no place that isheated to 800 K or more, an index of temperature at which breakage ofthe device is likely to occur. The ballast resistance region shares thecurrent, so that the diode 800A performs the breaking operation withoutbreakage. Thus, the breaking capability of the diode in the embodimentimproves.

FIGS. 41, 42A, and 42B show relationships between the widths L_(ABR),W_(p0) (FIG. 37) of the diode 800A and a temperature or a currentdensity inside the device at the time t_(d) (FIG. 39). As seen from theresults, L_(ABR)<W_(p0) needs to be set to suppress a concentration ofthe current density and a local temperature rise in order to improve thebreaking capability of the diode.

FIG. 43 shows relationships between a proportion γ of an area S_(abr) ofthe ballast resistance region to an area S_(active cell) (namely, thearea of the anode electrode 13) of the active area AR1 (FIG. 37) and amaximum breaking current density J_(A) (break) or an inside-devicemaximum temperature T_(max) during a recovery operation. In the exampleof FIG. 37, the area S_(abr) is substantially the same as the area ofthe interface area AR2, as shown in FIG. 44. J_(A) (break) is anexperimental result in the actual device, and T_(max) is a simulationresult. When γ is selected by the simulation such that T_(max) is set tobe less than or equal to 800 K (in a safety region SZ in the diagram),the actual device having high J_(A) (break) can be obtained.Specifically, it is clear that the high J_(A) (break) can be obtainedwhen γ is greater than or equal to 2% and less than or equal to 40%.

With reference to FIG. 37, the width W_(GR) is preferably set to begreater than the width W_(p0). To summarize the subject of theparameters, the relationships below need to be satisfied in order toincrease the breaking capability of the diode 800A.L _(ABR) <W _(p0)2%≤γ≤40%W _(GR) >W _(p0)

<Fourth Embodiment>

This embodiment gives descriptions of a diode having the sameconfiguration as the unit structure US in the IGBT 900G (FIG. 28)described in the second embodiment. In addition, part of thedescriptions of the same configuration as the IGBT 900G or the diode800A (FIG. 37) described above will not be repeated.

With reference to FIG. 45A, a diode 800B in this embodiment includes aninterlayer insulating film 12 a and an interlayer insulating film 12 bon an upper surface S1 of a substrate SB in an interface area AR2 and anedge termination area AR3. The substrate SB includes an anode layer 8D(impurity layer) that is provided on the upper surface S1 and has ap-type. The substrate SB includes a p⁻-extension region 9 j and aplurality of p⁻-field-limiting rings 9 g on the upper surface S1 in theedge termination area AR3. Similarly to the third embodiment, ann⁻-drift layer 1 is located on the inner side of each of thep⁻-field-limiting rings 9 g on the upper surface S1, and each of thep⁻-field-limiting rings 9 g together with the n⁻-drift layer 1 locatedon the inner side forms the unit structure US (FIG. 28). FIGS. 45B to45D respectively show diodes 800C to 800E being modifications. The diode800C (FIG. 45B) includes floating electrodes 13 e similarly to the IGBT900H (FIG. 35). In the diode 800D (FIG. 45C), an anode electrode 13extends to the p⁻-extension region 9 j with the interlayer insulatingfilms 12 a, 12 b therebetween, similarly to the gate connectingelectrode 13 b in the IGBT 900I (FIG. 36A). The diode 800E (FIG. 45D)has the structure of the diode 800D (FIG. 45C) from which the floatingelectrodes 13 e are omitted.

FIG. 46A shows waveforms of a voltage V_(AK) and a current density J_(A)during a recovery operation in each of the diode 800B as the embodiment(solid line) and the diode 800Z as the comparative example (brokenline), and FIG. 46B shows peak temperatures T inside the devices duringthe recovery operation. In the comparative example, when t=5.5 μs, anabrupt decrease in YAK and an abrupt increase in temperature to T>800 Koccur. In other words, breakage of the diode occurs in the middle of therecovery operation. In contrast, the break is completed without thebreakage in this embodiment.

FIGS. 47A to 47D respectively show a relationship between a position Xin a H-H′ line (FIG. 38) of the comparative example and surface electricfield strength E_(surface) when t=t₁ to t₄ (FIGS. 46A and 46B). FIGS.48A to 48F respectively show a relationship between a position X in aH-H′ line (FIG. 45A) of the embodiment and the surface electric fieldstrength E_(surface) when t=t₁ to t₆ (FIGS. 46A and 46B). FIGS. 49A to49D respectively show a relationship between the position X in the H-H′line of the comparative example and a current density j_(surface) whent=t₁ to t₄. FIGS. 50A to 50F respectively show a relationship betweenthe position X in the H-H′ line of the embodiment and the currentdensity j_(surface) when t=t₁ to t₆. FIGS. 51A to 51D respectively showa relationship between the position X in the H-H′ line of thecomparative example and a temperature T_(surface) of the upper surfaceS1 of the device when t=t₁ to t₄. FIGS. 52A to 52F respectively show arelationship between the position X in the H-H′ line of the embodimentand the temperature T_(surface) of the upper surface S1 of the devicewhen t=t₁ to t₆.

As seen from the results, the electric field strength in the interfacearea AR2 and the edge termination area AR3, particularly, the interfacearea AR2, during the recovery operation is lower in the embodiment thanthat in the comparative example, and the temperature rise in theinterface area AR2 is suppressed. Thus, the diode 800B conceivably hasthe high breaking capability similarly to the IGBT 900G. As a result,the effect of expanding the SOA can be obtained.

FIG. 53 is a graphical representation for describing recovery SOAs inthe comparative example (indicated by triangles) and the embodiment(indicated by circles). Herein, (dj/dt)_(max) represents a maximum valueof a time derivative of a current density allowable during the break,and P_(max) represents a maximum power density. The dj/dt value is aslope of a waveform of a current density in a region shown in, forexample, FIG. 46A, and the greater value allows the diode to perform therecovery operation at higher speed (that is to say, the breakingcapability during the recovery operation of the diode is higher). It isclear from the results that the recovery SOA improves since thisembodiment having the dj/dt value about three times as great as that inthe comparative example allows the recovery operation at higher speedand allows the break of the power density 50 times as great as that inthe comparative example.

The power semiconductor device in each of the embodiments isparticularly suitable for the high breakdown voltage class ofapproximately 3300 to 6500 V, but the amount of the breakdown voltage ofthe power semiconductor device is not particularly limited and may be,for example, greater than or equal to approximately 600 V. Further, thematerial for the semiconductor substrate is not limited to silicon andmay be wide band gap materials such as silicon carbide (SiC) and galliumnitride (GaN), for example. The first conductivity type and the secondconductivity type of the semiconductor substrate may be respectively then-type and the p-type and vice versa.

In addition, according to the present invention, each embodiment can beappropriately varied or omitted within the scope of the invention. Whilethe invention has been shown and described in detail, the abovedescription is the exemplification in all aspects and the presentinvention is not intended to be limited thereto. It is thereforeunderstood the numerous modifications and variations can be devisedwithout departing from the scope of the invention.

DESCRIPTION OF NUMERALS

1 n⁻-drift layer (drift region); 2 n-buffer layer (buffer layer); 3p-collector layer (collector region); 4 collector electrode (secondelectrode); 4D cathode electrode (second electrode); 5 n⁺-emitter layer;6 p⁺-layer; 8 p-base layer; 8D anode layer (impurity layer); 9 p-guardring; 9 a p-well region; 9 b p-edge region; 9 g p⁻-field-limiting ring;9 j p⁻-extension region; 10 trench insulating film; 11 gate electrode;12, 12 a, 12 b interlayer insulating film; 13 anode electrode (firstelectrode); 13 a emitter electrode (first electrode); 13 b gateconnecting electrode; 13 c, 13 d electrode; 13 e floating electrode; 14,15 passivation film; 22 gate electrode; 22 w gate wiring layer; 23capacitor electrode; 24 n-layer; 26 p-layer; 27 n⁺-layer; 28 gate wiringportion; 29 gate pad; 32 channel stop electrode; 34 n-region; 35n⁺-region; 38 p-region; 800A, 800B diode; 900A to 900I IGBT; AR1 activearea; AR2 interface area; AR3 edge termination area; CS channel stopstructure; S1 upper surface (first surface); S2 lower surface (secondsurface); SB substrate (semiconductor substrate); TC capacitor trench;TG gate trench; TS channel stop trench; US, US1 to US6 unit structure.

The invention claimed is:
 1. A power semiconductor device having anactive area, an interface area provided around a periphery of saidactive area, and an edge termination area provided around a periphery ofsaid interface area, said power semiconductor device comprising: asemiconductor substrate having a first surface and a second surfaceopposite to said first surface, said first surface and said secondsurface each being located across said active area, said interface area,and said edge termination area, said semiconductor substrate including adrift region that is provided across said active area, said interfacearea, and said edge termination area and has a first conductivity type,a well region that is provided on said first surface, is at leastpartially included in said interface area, has an end portion on saidfirst surface between said interface area and said edge terminationarea, and has a second conductivity type different from said firstconductivity type, an extension region that extends outward from saidwell region on said first surface, is shallower than said well region,and has said second conductivity type, and a plurality of field-limitingrings that are provided on said first surface outside said extensionregion in said edge termination area and have said second conductivitytype, said drift region being located on the inner side of each of saidfield-limiting rings on said first surface, each of said field-limitingrings together with said drift region located on the inner side thereofforming a unit structure, one of said field-limiting rings locatedcloser to the outside has a lower proportion of a width to a width ofsaid unit structure than another of the field-limiting rings locatedinward from said field-limiting ring located closer to the outside, eachsuccessive unit structure is adjacent to a previous unit structure in adirection from the active area towards the outside along said firstsurface of said semiconductor substrate, said unit structure locatedcloser to the outside having a lower average dose; a first electrodethat is provided in said active area and contacts said first surface ofsaid semiconductor substrate; and a second electrode contacting saidsecond surface of said semiconductor substrate, wherein each of saidunit structures on said first surface of said semiconductor substratehas a fixed width (W_(cellpitch)).
 2. The power semiconductor deviceaccording to claim 1, wherein said semiconductor substrate includes acollector region being provided only in said active area, forming partof said second surface, and having said second conductivity type, saidsecond surface in said edge termination area only having said firstconductivity type.
 3. The power semiconductor device according to claim2, wherein said collector region has an area accounting for greater thanor equal to 55% and less than or equal to 70% of said second surface ofsaid semiconductor substrate.
 4. The power semiconductor deviceaccording to claim 1, wherein said first surface of semiconductorsubstrate has an electrical path formed thereon, said electrical pathconnecting said first electrode to said end portion of said well regionwith a region of said second conductivity type, said electrical path hasa ballast resistance region that is formed of said well region and has awidth L, and the width L is set so as to cause a local temperature riseat both ends of said ballast resistance region during a breakingoperation of said power semiconductor device.
 5. The power semiconductordevice according to claim 4, wherein the width L is greater than orequal to 100 μm.
 6. The power semiconductor device according to claim 4,wherein said first surface of said semiconductor substrate in saidactive area has an area S_(act), said ballast resistance region on saidfirst surface of said semiconductor substrate in said interface area hasan area S_(abr), and the area S_(abr) is greater than or equal to 2% andless than or equal to 40% of the area S_(act).
 7. The powersemiconductor device according to claim 1, further comprising a floatingelectrode provided on each of said field-limiting rings.
 8. The powersemiconductor device according to claim 1, further comprising: aninterlayer insulating film covering said extension region; a gateelectrode; and a gate connecting electrode that is provided on saidextension region with said interlayer insulating film therebetween andis short-circuited to said gate electrode.
 9. The power semiconductordevice according to claim 1, further comprising: a floating electrodeprovided on each of said field-limiting rings; an interlayer insulatingfilm covering said extension region; a gate electrode; and a gateconnecting electrode that is provided on said extension region with saidinterlayer insulating film therebetween and is short-circuited to saidgate electrode.
 10. The power semiconductor device according to claim 1,wherein said semiconductor substrate includes an impurity layer that isprovided on said first surface and has said second conductivity type,said power semiconductor device further comprising an interlayerinsulating film covering said extension region, a first electrode havinga portion contacting said impurity layer in said active area and aportion located on said extension region with said interlayer insulatingfilm between said extension region and said first electrode, and asecond electrode provided on said second surface of said semiconductorsubstrate.
 11. The power semiconductor device according to claim 1,wherein said semiconductor substrate includes an impurity layer that isprovided on said first surface and has said second conductivity type,said power semiconductor device further comprising a floating electrodeprovided on each of said field-limiting rings, an interlayer insulatingfilm covering said extension region, a first electrode having a portioncontacting said impurity layer in said active area and a portion locatedon said extension region with said interlayer insulating film betweensaid extension region and said first electrode, and a second electrodeprovided on said second surface of said semiconductor substrate.